1. Field of the Invention
This invention relates to a pre-mastered pit/pre-mastered groove discriminator circuit for discriminating a pre-mastered pit area and a pre-mastered groove area on an optical disk, particularly a recordable magneto optical disk.
2. Description of the Related Art
In recent years, MDs (mini disk) have been proposed which are half the size of CDs (compact disk). An MD, which is a magneto optical disk, is not only reproducible but also recordable using light and magnetism.
Such a recordable ND has a structure in which pre-mastered pits similar to those on a CD are scored on an inner circumferential part of the MD and pre-mastered grooves are spirally formed on an outer circumferential part outside the pre-mastered pit area so that data can be recorded along a pre-mastered groove. In recording signals on the MD, firstly a light pickup traces the pre-mastered pit portion to pick up data indicating a recording condition and then traverses the pre-mastered pit and pre-mastered groove rows, whereupon the light pickup has to be positioned on the pre-mastered groove. In the conventional art, however, since the pre-mastered pit/pre-mastered groove discrimination was impossible during traversing, it was necessary to move the light pickup to a midportion of the pre-mastered groove and then to locate it at the end of the pre-mastered groove so that it would take a long time to start recording.
Having a difference in radial tracking signal, i.e. reflection factor, between pre-mastered pits and pre-mastered grooves, in order to employ a suitable servo control, it is necessary to discriminate as to whether the pre-mastered pit portion or the pre-mastered groove portion is being tracked. To this end, a circuit shown in FIG. 1 of the accompanying drawings has hitherto been proposed for carrying out pre-mastered pit/pre-mastered groove discrimination during tracking. In FIG. 1, output signals of a light receiving element pass through first and second coupling capacitors 3, 4 via their respective input terminals 1, 2 and are then added in an adder circuit 5 using a differential amplifier to form an RF signal. The RF signal is applied to a peak hold circuit 7 via a third coupling capacitor 6 so that a peak value of the RF signal is held. The output signal of the peak hold circuit 7 is compared with a reference value in a comparator circuit 8 which then generates an output signal `1` or `0` according to the result of comparison.
However, the pre-mastered pit/pre-mastered groove discriminator circuit of FIG. 1 cannot perform a pre-mastered pit/pre-mastered groove discrimination during traversing and hence cannot be used to discriminate the start time for recording. Specifically, during traversing, at both the pre-mastered pit and pre-mastered groove areas, an output signal is generated from the adder circuit 5 and a peak value of the output signal is held by the peak hold circuit 7. According to the output signal from the peak hold circuit 7, the comparator 8 generates the signal `1`. That is, no discrimination can be performed during traversing.